1. Field of the Invention
This invention relates to a zoom lens assembly, and more particularly to the structure of the barrel of a zoom lens system in which a first group is a stationary lens group relative to movable lens groups shifted for focusing and zooming.
2. Description of the Prior Art
In the conventional zoom lens barrel of a construction in which a first lens group is shifted in the direction of the optical axis for focusing, the torque necessary for focusing operation has been great for the movement of the first lens group which has a relatively large lens diameter, and the operability has been poor because the operating portion is moved with the shift of the first lens group, and further, the position of the center of gravity of the entire lens barrel has been greatly varied. Particularly, zoom lenses of long focal length have suffered from the disadvantage that when mounted to cameras, they are difficult to use in the photographing operation.
For this reason, zoom lens optical systems in which the first lens group is stationary are proposed, for example, in U.S. Pat. No. 4,110,006, etc. and have been attracting attention in recent years.